This application is a divisional application of U.S. application Ser. No. 12/330,850, filed Dec. 9, 2008.
1. Field:
The present disclosure relates generally to manufacturing and, in particular, to a method and apparatus for manufacturing parts. Still more particularly, the present disclosure relates to a method and apparatus for manufacturing parts in which exothermic reactions may be present.
2. Background:
Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Some aircraft may have more than fifty percent of their primary structure made from composite materials. Composite materials may be used in aircraft to decrease the weight of the aircraft. This decreased weight may improve performance features, such as payload capacities and fuel efficiencies. Further, composite materials may provide longer service life for various components in an aircraft.
Composite materials are strong, light-weight materials, created by combining two or more dissimilar components. For example, without limitation, a composite may include fibers and resins. The resin may be in the form of a substrate or matrix. The fiber may form a reinforcement for the substrate. For example, without limitation, the fibers may take the form of a woven cloth or a uni-directionally oriented ply of fibers. The fibers and resins may be combined and cured to form the composite material.
Further, by using composite materials, portions of an aircraft may be created in larger pieces or sections. For example, without limitation, a fuselage in an aircraft may be created in cylindrical sections that may be put together to form the fuselage of the aircraft. Other examples include, for example, without limitation, wing sections joined to form a wing or stabilizer sections joined to form a stabilizer.
In manufacturing composite parts from composite materials, the composite materials may be cured to form the composite parts. In curing composite materials, processes may be present that involve exothermic reactions.
Under certain conditions, these reactions may become unstable and/or uncontrolled when heat from the reaction is generated faster than the heat can be dissipated to the surroundings. In these types of situations, the temperature of the process rises in a manner that may be undesirable.
For example, without limitation, if the curing process should be performed at around 350 or 355 degrees, some exothermic reactions during the curing process may cause the temperature to exceed an allowable tolerance. The tolerance may be plus or minus 10 degrees Fahrenheit. It is undesirable for the temperature to exceed the upper limit for a curing process. If the temperature during the curing process exceeds the upper limit or tolerance, the particular composite part may be rejected.
This type of exothermic reaction is currently controlled in a number of different ways. For example, without limitation, the heating rate may be slowed to slow the reaction and allow greater time for the heat to dissipate. This type of process, however, may extend the cure cycle by many hours. As a result, equipment used to cure composite parts may be unavailable for long periods of time, therefore reducing the throughput and/or increasing the cost to manufacture composite parts.
Another solution may include inserting a dwell segment into the cure cycle at an intermediate temperature to allow the exothermic reaction to occur at a lower temperature, such that the effect is not undesirable to the part. One drawback of this type of process is that inserting a dwell segment is often not allowed under the procedures and specifications for manufacturing composite parts. Heat sinks also may be used with a tool to control heat flow or absorb excess heat. Heat sinks, however, typically are capable of absorbing excess heat but are seldom used because the heat sinks also slow heating rates needed for the curing process.
The part may be cured multiple times in which the thickness of the part may be increased in stages, such that the temperature tolerance is not exceeded. Curing a part multiple times, however, may require a bond line of adhesive within the structure. This bond line may have undesirable properties.
Thus, it would be advantageous to have a method and apparatus that addresses one or more of the issues discussed above.